The invention relates to an improved headlight for motor vehicles U.S. Pat. No. 4,513,356 discloses a headlight of this kind, made of plastic. In this patent, a locking means is detachably fastened to the outer jacket of the crown neck by means of a bayonet connection, the required grooves being cut out of the outer jacket. To produce these grooves, an injection tool for the reflector requires a plurality of lateral slides, which presents technical difficulties, especially when thermosetting plastics are used.